Did you trust your roofer to install your attic ventilation correctly, only to find out later that your attic has mold, condensation, or moisture problems? Wondering how you’re supposed to know whether your ventilation meets Seattle-area building code when everything looks perfectly fine from the outside?
At RoofSmart, we’ve inspected hundreds of Seattle-area roofs where the ventilation was installed incorrectly or laid out in a way that prevents air from actually moving through the attic. In most cases, the homeowners have no idea there’s a problem until we get into the attic and find mold or other signs of trapped moisture. This is because most roofers don’t inspect attic ventilation.
In this case study, I will explain what building code requires for attic ventilation, show you a real example of how improperly placed exhaust vents can short-circuit airflow, and help you understand what to look for to determine whether your roofer ventilated your attic correctly.
Unfortunately, a lot of roofers in the Seattle area are unfamiliar with building code standards for attic ventilation. This means that your roof likely does not have proper ventilation, which leads to other issues on your roof.
This type of issue is something that I see all of the time when I meet with customers. They will call us up and ask for an inspection because their roof is getting old, and then when I get out there, I usually notice that their attic ventilation is all wrong.
For example, I recently inspected a roof that had a large cluster of RVO vents on one side of the roof. This type of vent is a static vent used for exhaust ventilation. Here’s what it looked like:
An RVO vent is not an uncommon choice for Seattle roofs, but the problem on this house is that they were all clustered together.
These vents have a certain amount of venting power, so they need to be spread out accordingly. In this setup, there are far too many of them in the same area. As a result, the airflow short-circuits.
This means that instead of air flowing in from the intake vents along the bottom of the roof and upward out of these RVO vents, air starts being sucked in and out of the RVO vents. It completely bypasses the intake vents.
Air is not flowing properly through the attic. In fact, it’s barely flowing at all. This lack of airflow often leads to attic mold, and this case was no exception. In this image, you can see that the lower portion of the attic has mold:
That black stuff isn’t a shadow. It’s mold, which shows that air is not flowing in that area. This highlights the other major ventilation problem in this attic: the intake vents are blocked by insulation, so little to no air is entering the attic.
The poor ventilation in this attic caused mold and reduced the lifespan of the shingles. This customer is just one of many homeowners in Seattle and the surrounding areas who unknowingly had major attic ventilation issues.
The real problem here is roofers who don’t view attic ventilation as part of their job because they are setting homeowners up for failure.
Since so many roofers ignore attic ventilation (either because they don’t know about it or they don’t care), the average roofer probably won’t say anything about your attic ventilation during their inspection. Hardly any roofers even look in the attic.
At best, the average roofer might mention replacing your ridge vent or static vents (whatever you have already) while they replace the roof, but only because all the old vents will be torn off.
Despite having a large grouping of RVO vents on their roof, this customer said that no other roofers that they hired to come out for an inspection mentioned anything about attic ventilation.
Out of the 7 to 8 companies that they had out to their house, I was the only one to talk to them about attic ventilation. They had no idea that it wasn’t working and that they had mold until I told them. None of the other companies even looked in the attic.
Due to my thorough roof inspection and suggestions for fixing their attic ventilation, the customer chose to hire RoofSmart instead of the other companies.
If you need your roof replaced and you want to make sure that your roofer inspects your attic ventilation system while checking out your roof, then you’ll have to do some extra research. Roofers who care about attic ventilation (like us at RoofSmart) are out there; it’s just hard to find them sometimes.
Fixing attic ventilation issues can look drastically different on every roof. In this case, we added baffling around the outer edges of the roof to let air into the attic. The crew also installed an electric fan to replace all the static vents.
This combo ensures that air can flow through the entire attic properly. Plus, their intake and exhaust ventilation is balanced. Now that this customer finally has proper ventilation in their attic, they don’t have to worry about the mold coming back.
We also removed the roof decking boards with mold on them and performed mold remediation to get rid of any lingering spores.
After that, we replaced the missing roof decking with new plywood and installed new shingles on the roof. The customer was very pleased to have a new roof and relieved to know that it was set up to last as long as possible by updating the attic ventilation.
|
Attic Ventilation Issue |
What Happens |
Potential Consequence |
How It Can Be Corrected |
|
Exhaust vents are clustered together |
Air can move in and out of nearby exhaust vents instead of traveling through the attic |
Poor airflow and areas of stagnant air |
Space exhaust ventilation appropriately or redesign the exhaust system |
|
RVO vents short-circuit airflow |
Air bypasses the intake vents instead of entering low and exhausting higher on the roof |
The attic receives little effective airflow |
Correct the exhaust ventilation setup so air moves through the entire attic |
|
Intake vents are blocked by insulation |
Little to no outside air can enter through the intake vents |
Mold can develop in poorly ventilated areas |
Add baffling to keep insulation from blocking airflow |
|
Intake and exhaust are not balanced |
Air does not move properly through the attic |
Moisture and heat can become trapped |
Design the system so intake and exhaust ventilation work together |
|
Attic ventilation isn't inspected |
Existing ventilation problems can go unnoticed during roof replacement |
A new roof may be installed without correcting the underlying ventilation problem |
Have the roofer inspect the attic and ventilation system before replacing the roof |
|
Mold has developed on roof decking |
Moisture caused by poor airflow affects the decking |
Mold can continue to be a problem even after ventilation is corrected |
Remove affected decking when necessary and perform mold remediation |
|
Existing ventilation system isn't working |
The attic does not receive consistent airflow from intake to exhaust |
Mold problems and reduced shingle lifespan |
Redesign the ventilation system for the specific roof and attic |
If your attic ventilation was installed incorrectly, then the vents on your roof are not actually doing their job. As we’ve seen, exhaust vents that are improperly sized, positioned, or clustered together can disrupt airflow and leave parts of your attic vulnerable to trapped moisture and mold.
That’s why it’s important to understand what proper attic ventilation should look like before assuming your roofer got it right. Knowing the requirements can also help you ask better questions when getting your roof inspected or replaced.
So, how much ventilation does your attic actually need, and where should those vents be installed?
Read our article “What Are Seattle’s Attic Ventilation Code Requirements?” to learn how attic ventilation is calculated, what Seattle-area building code requires, and how to determine whether your ventilation system is set up correctly.